1. Field of the Invention
This invention relates to an automatic transmission control system in which shift control is accomplished on the basis of shift characteristics according to vehicle speed.
2. Description of Related Art
Some automobile engines are provided with an electric throttle valve, which is operated by an electric motor, in addition to a mechanical throttle valve, which opens and closes in response to movements of the accelerator pedal. Since the electric throttle valve is controlled to show more tendency toward closing, the engine output is virtually controlled by the electric throttle valve. Such an automobile engine is known from, for instance, Japanese patent application No. 1-44,013, entitled "Throttle Opening Control System Of Engine Intake System," filed on Feb. 23, 1989 and now opened as Japanese Unexamined Patent Publication No. 2-221,658 on Aug. 4, 1990.
Automatic transmissions for use with this kind of engine are typically controlled on the basis of shift patterns, such as shown in FIG. 1, according to throttle opening and vehicle speed. With most of such automatic transmissions, although attempts are made at establishing optimal shift patterns for the most efficient fuel consumption corresponding to engine output, it is difficult to establish shift patterns that satisfactorily meet all requirements due to the fact that the opening of an electric throttle valve, with which actual engine output is controlled, will vary depending upon various driving conditions as is shown by the shaded area in FIG. 2.